Furnace and method for heating and compacting powdered metal charges

ABSTRACT

A furnace, for use in heating charges of powdered metal to compacting temperatures, having an elongated vertically disposed furnace chamber surrounded by heat-insulating material with a lid positioned at the top of said furnace. With the lid in the open position the powdered metal charge to be heated may be vertically inserted and withdrawn from the chamber. For this purpose a pedestal connected to a shaft is movable to a position adjacent the furnace chamber top to receive the charge for heating and may be lowered to a postion near the bottom of the furnace chamber during heating of the charge. The overall furnace arrangement permits the rapid withdrawal of the heated furnace charges for transportation to a compacting means such as an autoclave by a conventional overhead crane.

United States Patent [191 Kinsch, Jr. et al. July 3, 1973 [54] FURNACE AND METHOD FOR HEATING 2,980,415 4/1961 Beard., 266/5 R AND COMPACTING POWDERED METAL 2,332,943 /1943 Sobers 266/5 R CHARGES Primary Examiner-Gerald A. Dost [75] Inventors: Anton H. Klnsch, Jr., Camlllus; c XI Mullen William M. Rogers, Liverpool; Robert A Lake, Syracuse, all, Assigneei Crucible Pittsburgh, A furnace, for use in heating charges of powdered 22 d: l 21 1971 metal to compacting temperatures, having an elon- 1 l 6 y gated vertically disposed furnace chamber surrounded PP ,725 by heat-insulating material with a lid positioned at the top of said furnace. With the lid in the open position [52] Us. CL 266/24 75/214 the powdered metal charge to be heated may be verti- [51] Int CL I F27b 17/00 cally inserted and withdrawn from the chamber. For [58] Field 2 R this purpose a pedestal connected to a shaft is movable 26376 to a position adjacent the furnace chamber top to receive the charge for heating and may be lowered to a 56] References Cited postion near the bottom of the furnace chamber during heating of the charge. The overall furnace arrangement UNITED ST ATES PATENTS permits the rapid withdrawal of the heated furnace 747,019 12/1903 Swindell 263/6 R charges f transportation to a compacting means h K Z g g as an autoclave by a conventional overhead crane. m er 1,844,604 2/1932 Schwab 266/5 R 32 Claims, 6 Drawing Figures 1' a t W 471/" 4 f has? a; f 6 30 9 1 0 U/77' E o o 74 0 L I I" ,0

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Attorney FURNACE AND METHOD FOR HEATING AND COMPACTING POWDERED METAL CHARGES In the powder metallurgy art wherein metal in powdered form is heated to an elevated temperature and while at said temperature subjected to pressure to form dense metal compacts, it is well known to perform this operation by the use of a fluid pressure vessel, commonly termed an autoclave, a typical example of which is shown in Boyer US. Pat. No. 3,543,345, Dec. 1, 1970. By the use of an autoclave, as opposed to mechanical compacting, more uniform pressure application is achieved and with many powdered metal products, such as tool-steel articles, the quality of the product is greatly improved as a result of this uniform pressure application.

Many powdered metal articles, and particularly tool steels, must be compacted at extremely high temperatures. For tool steels, the compacting temperature may be typically within the range of 1,800 to 2,200 F. To achieve these compacting temperatures the powdered metal charge, prior to compacting, must be heated for long times, typically on the order of about three hours or more. With prior art practice this heating has been performed in the autoclave and upon reaching compacting temperature the autoclave is pressurized to'effect compacting of the powdered metal charge to the required high density. in view of the long heating times, however, this practice is not economically feasible because the autoclave production is severely limited. Alternately, therefore, it is desired to heat the powdered metal charge to compacting temperature within a fur nace separate from but located adjacent to the autoclave. When the charge has been heated to compacting temperature or slightly above, it is rapidly transported to'the autoclave, which may be that identified in the above-mentioned Boyer patent, and quickly compacted by the application of fluid pressure before cooling below the selected compacting temperature for the particular alloy composition. The autoclave generally is loaded vertically by the use of an overhead crane. To rapidly transport the heated charge from the furnace to the autoclave it is desirable to load and unload the furnace by the use of the same overhead crane so that the overall operation comprising removing the heated charge from the furnace and loading it into the autoclave may be continuous. In this manner compacting may be achieved at a time after removal of the charge from the furnace of sufficiently brief duration that the charge does not cool below the desired compacting temperature. Otherwise, it is necessary to provide for auxiliary heating means, such as electrical resistance heating elements, within the autoclave to provide auxiliary heating necessary to maintain the charge at compacting temperature. As is well known, this not only adds to the cost and complexity of operation of the autoclave but in addition lengthens the compacting cycle within the autoclave, thereby reducing the production capacity of the autoclave and correspondingly increasing the cost of the overall compacting operation and final compacted product.

It is accordingly a primary object of the present in vention to provide a furnace, particularly adapted for heating a powdered metal charge to compacting temperature, that permits rapid charging of the furnace with a powdered metal charge for heating and rapid withdrawal of a heated charge therefrom by the use of an overhead crane; the same crane then carries the heated charge upon withdrawal from the furnace directly to the autoclave for compacting.

This and other objects of the invention, as well as a complete understanding thereof, may be obtained from the following description, specific examples and drawings in which:

FIG. 1 is an elevation view in partial vertical section of one embodiment of a furnace in accordance with the present invention;

FIG. 2 is a plan view of the furnace;

FIG. 3 is a horizontal section taken along lines III-Ill of FIG. 1;

FIG. 4 is an elevation view of a portion of the furnace in partial section taken along lines IV-IV of FIG. 3;

FIG. 5 is an enlarged, detailed view of a portion of the furnace as shown in FIG. 2; and

FIG. 6 is a schematic showing of a typical air rotary actuator preferred for use in association with the furnace.

Broadly, the furnace of the present invention includes an elongated, vertically disposed furnace chamber surrounded by a suitable refractory lining to provide for heat insulation. Atop the furnace is a lid which is selectively positionable between open and closed po sitions, whereby a powdered metal charge may be vertically inserted and vertically withdrawn with respect to said furnace chamber typically by the use of a conventional overhead crane or the like. A pedestal is pro vided within the furnace chamber and is movable between positions adjacent the lid and uppermost portion of the furnace, and the bottom of the furnace chamber. With the pedestal adjacent the lid, an overhead crane may set a powdered metal charge for heating on the pedestal, the pedestal may be lowered to the bottom of the furnace chamber, the lid closed and the charge heated to an elevated temperature desired for subsequent compacting, as by the use of an autoclave.

The pedestal is preferably connected to an end of a vertically extending shaft with associated drive means for moving the shaft axially within said furnace chamber and toward either the top or the bottom of the chamber. The shaft preferably has means for circulation of a coolant, such as water, therein to protect the shaft against heat damage during movement within the furnace chamber. The drive means includes a counterweighted chain connected to the end of the vertically extending shaft opposite that to which the pedestal is connected, with the chain extending over a pulley positioned intermediate the counterweight and the connection of the chain to the shaft. The vertically spaced guides, which preferably are a plurality of idler rolls, are provided in association with the shaft for guiding it during movement. The pedestal, which is connected to the upper end of the shaft includes a core of heat insulating material atop which the charge is supported for heating. By this arrangement, with the pedestal in the position adjacent the bottom of the furnace during heating of the charge heat transfer through the pedestal is minimized.

Although various means may be used for supplying heat in the furnace, it is preferred to use a plurality of resistance heating elements in the form of parallel rods with the resistance heating elements being provided along the entire length of the furnace chamber. For most effective temperature control within the furnace chamber, means may be provided for independently applying electrical current to selected heating elements over locations adjacent the mid-portion and ends of the furnace chamber. Associated therewith may be means for determining the temperature of the furnace chamber at each area of independent supply of electrical current, so that upon independent temperature mea surement at the selected area the supply of electrical current to the associated resistance heating elements at the areas may be regulated to provide a desired temperature profile along the length of the furnace chamber. This arrangement is particularly advantageous for maintaining uniform temperature along the entire length of the furnace chamber.

The top of the furnace chamber is preferably provided with a unitarily removable top assembly. This top assembly is mounted on top of the refractory lining surrounding and defining the furnace chamber, which is preferably annular. With this arrangement the top may be unitarily removed to expose the refractory for inspection, repair and efficient furnace relining. The top assembly preferably has a core of heat insulating material surrounding and defining an orifice in axial alignment with the vertical furnace chamber; the orifice is selectively opened and closed by the furnace lid. To facilitate sealing upon closing of the lid it is preferred that the orifice be annular and tapered axially and inwardly toward the furnace chamber axis, with the lid being correspondingly tapered. To facilitate rapid opening and closing of the lid it is preferred that it be in two movable sections with each section being provided with means for simultaneously moving the sections upwardly and out of engagement within the orifice and away from the axis thereof. This is achieved by providing for each section a pivot link connected at one end to a drive shaft and at the opposite end to a=pivotal connection to said section. With this arrangement the lid is out of the way when in the open position so that it is not subject to damage during insertion and removal of furnace charges as by the use of an overhead crane. Preferably an independent drive for each section of the lid is provided. By this arrangement the opening and closing of each lid section may be sequenced somewhat out of phase, which insures smooth operation by avoiding hang-up during adjacent movement of the sections. Each section of the lid preferably includes two parallel spaced apart plates separated by a core of heat insulating material with means, such as tie bolts, for securing said heat insulating material between the plates. Each section is counter-weighted to compensate for its weight to minimize the drive required during opening thereof. Also the lid should when in the closed position provide an opening therein to the exterior of the furnace through which may extend a stem communicating with the interior of a container when positioned in the furnace, said container holding the powdered metal charge for heating. I

With reference to the drawings and for the present to FIGS. 1 and 2 thereof, there is shown a furnace assembly in accordance with the present invention and idenchannels is an upper plate 24 and a lower plate 26. Each plate 24 and 26 has concentric annular openings 28 and 30, respectively, therein and axially aligned with the furnace chamber. The opening 30 is of lesser diameter than opening 28 to provide for a tapered orifice 32 defined by a casta'ble refractory 34 constituting a core between plates 24 and 26.

In association with the removable top assembly 20 is provided an annular, two-section lid indicated generally as 36. The lid 36 consists of two identical half sections each including two parallel spaced-apart upper and lower plates 38 and 40, respectively. Between the plates is provided packed insulating material 42. The heat insulating material 42 is secured as a core between plates 38 and 40 by a plurality of tie bolts 44 connected at opposite ends to plates 38 and 40 and extending through heat insulating material 42. By loosening the tie bolts 44, the plates 38 and 40 may be detached from the heat insulating material 42 to permit replacement thereof.

As best shown in FIGS. 2 and 5, to the surface of veach plate 38 of each lid section there is connected a trunnion 46. The trunnion is connected to the plate by bolts 48. The trunnion journals shaft 50 connected to an upstanding pivot ear 52. Adjacent the ends of shaft 50 is connected pivot links 54 which are pivotally connected as at 56 to shaft 50 and at 58 to a second parallel shaft 60. Shaft 60 is drivingly connected to a motor 62. Shaft 60 is also connected to a sprocket 61. Associated therewith is sprocket 63 journaled on a fixed shaft 67. A continuous chain 69 is connected between these sprockets 61 and 63. One end of an arm 71 is connected to sprocket 63 and the other end to a pin 73 which extends through the arm in a manner permitting free axial rotation of the pin. Adjacent each end of pin 73 are connected opposed links 75, which connect counterweight 77 to the arm and allow free rotation thereof with respect to arm 71. Although only one counterweight arrangement has been shown in FIG. 2, duplicate structure is provided for each section of the lid. As earlier explained, the counterweight 77 minimizes the drive required to open each section of the lid. Preferably the motor 62 is a conventional air rotary actuator, which is shown schematically in FIG. 6. Broadly such apparatus comprises a rack and pinion arrangement wherein movement is imparted to the rack by application of compressible fluid, preferably air. The rotary air actuator consists of opposed parallel racks 64 each engaging pinion gear 66. The opposed ends of each rack 64 are connected to air cylinders 68. Upon introduction of air to one of the two opposed air cylinders 68 the rack is correspondingly moved to cause rotation of pinion 66. Pinion 66 is connected to shaft 60 and consequently rotates the shaft in the direction of pinion rotation. In this manner by the operation of the air rotary actuator 62 the shaft 60 may be rotated in the direction appropriate to either open or close the associated lid section.

By the rotation of shaft 60 in a counterclockwise di rection through pivot links 54 connected to shaft 50 the lid section is moved a distance axially upwardly and then away from the furnace chamber axis to an open position, as indicated by the dashed lines in FIG. 2. With both lid sections in the position indicated by the dashed lines in FIG. 2 the furnace chamber is open at the top to permit charges to be inserted or withdrawn. The lid'sections are sufficiently out-of-way that they are not subject to damage during this operation. By rotating the shaft in the opposite direction the lids are in like manner brought to the closed position. The lid sections when in the closed position define a small central orifice extending from the exterior to the inte rior of the furnace chamber.

The furnace chamber is heated by a series of resistance heating elements 72 extending through the refractory furnace lining 18 to connector boxes 74. Within connector boxes 74 electric leads 76 are connected to the resistance heating elements. Preferably separate leads are provided for elements adjacent the top, mid-portion and bottom portion of the furnace chamber. This is indicated in FIG. 1 by independent electrical connections through separate lead wires 76 to individual, single resistance heating elements 72 at the top, mid-portion and bottom portion. However, it is to be understood that in actual practice each lead wire or independent electrical connection would connect with a plurality of heating elements, rather than a single heating element, at each portion of the furnace. In this manner, by independently varying the electrical current through each lead wire independent temperature regulation at the ends and mid-portion of the furnace may be achieved. The resistance heating elements '72 could be of any configuration but are preferably rods horizontally disposed in parallel spaced-apart relation along the length of the furnace chamber as shown in FIG. ll. The temperature of the furnace may be monitored at the ends and mid-portion thereof by directing a temperature-measuring device, such as an optical pyrometer, through each sight hole 73 provided through the furnace wall.

Although the furnace charge provided for heating in the furnace may be of any configuration, typically the powdered metal charge will be confined within a cylindrical steel container 78, as shown in FIG. 1. The container 78 has a stem 80 which extends through orifice 78 in the lid to the exterior of the furnace withthe container 78 being positioned as shown in FIG. 1. This permits, via stem 80, the interior of the container 78 to be connected to avacuum pump or the like as for outgassing and the like of the container interior in the conventional manner prior to or during heating. Also, typically the container 78 will be surrounded by a heat insulating casing 82 connected at the bottom to a stool 84, by means not shown. The heat insulating casing 82 minimizes heat loss upon removal of the heated container 78 and during its transfer from the furnace after heating to the compacting means, such as an autoclave. A suitable heat insulating casingarrangement for this purpose is shown Patent Application Ser. No. 772,681, filed Nov. 1, I968 now US. Pat. No. 3,599,281, issued Aug. 7, 1971.

The powdered metal container 78 and associated heat insulating casing 82, as shown in FIG. 1, rest on a vertically movable pedestal 86. The pedestal 86 comprises a casing in the form of a cylinder of heat resistant alloy, such as Inconel. The interior core ofthe pedestal 86 comprises a castable refractory 90. The bottom of the pedestal 86 has a plate 92 centrally connected to a shaft 94. The shaft 94 is provided with a bore 96 through which a coolant, such as water, may be circulated to protect the shaft from heat damage whenit is in the interior of the furnace chamber. The shaft is movable axially to position the pedestal either adjacent the bottom of the furnace chamber, which is the position shown in FIG. 1 during heating of the charge, or adjacent the top of the furnace chamber, which is the position from which the charge is either placed by an overhead crane on a pedestal or removed therefrom after heating. Axial movement of the shaft 94 is provided by a motor 98 which may be an air rotary actuator as shown and described in connection with FIG. 6. This motor has a shaft 100 connected to sprocket 102 which is in turn connected to shaft 104 of a pair of pulleys 106 by a continuous chain 1'08. Counterweighted connecting chains 1118 are connected at one end to counterweights 1112 and at the opposite end to the bot tom of shaft 94 as at 114. Therefore, upon rotation of the shaft 100 of motor 98 the shaft 104 is correspondingly rotated via its connection to shaft 100 by chain 108 to rotate pulleys 106 which through chains 110 selectively provide for the axial movement of shaft 94 toward and away from the furnace chamber.

During this movement of shaft 94 counterweight 112 during associated movement is guided vertically by channel guides 116, as shown in FIGS. 3 and 4. Shaft 94 is guided during the vertical movement thereof by idler rolls 118, shafts of which are journaled in bearings 12]. fastened to vertical columns 122.

By way of summary of the operation of the furnace a powdered metal charge within container 78, which is enclosed by heat insulating casing 82 as previously de scribed, is lifted by means such as a conventional overhead crane (not shown) and with the lid 36 provided in the open position in the manner described hereinabove, the container is lowered substantially vertically onto the pedestal 86. The pedestal 86 is during this operation at the position adjacent the uppermost end of the furnace. When the container 78 has been set on the pedestal 86 it is lowered, in the manner described hereinabove, vertically within the furnace chamber to a position adjacent the lowermost end of said furnace chamber. This is the position of the pedestal 86 and container 78 as shown in FIG. I of the drawings. At this time the lid is brought to the closed position with the stem 80 of container 78 extending through orifice 70 of the lid to the exterior of the furnace. As is conventional at such time gaseous reaction products may be removed from the container interior by communicating the same via the stem 80 to a pump. As is conventional, an inert gasmay be introduced to the interior of the stem, via a stem 80, to accelerate heating. Heating is, of course, effected by applying electrical current through lead wires 76 to resistance heating elements 72. Upon heating of the charge within container 78 to a selected compacting temperature within the furnace chamber, the lid is again brought to the open position, the pedestal with the container 78 thereon is raised vertically again to the position adjacent the uppermost end of the furnace and the container with the heat insulating casing attached thereto is raised from the pedestal as by the use of an overhead crane and moved to compacting means constituting a fluid pressure vessel providing for top loading of the container 78, as shown in Boyer et al. US. Pat. No. 3,543,345. The crane lowers the container substantially vertically into the fluid pressure vessel and while the charge is at an elevated temperature fluid pressure is applied to the container in the well-known manner to compact the powdered metal charge therein. After compacting the container is again removed by the overhead crane substantially vertically from the pressure vessel. The container is removed from the powdered metal compact to ready the compact for further processing.

It may be seen from the description of the overall operation that the furnace of the invention enables continuous, overhead loading of a powdered metal charge into the furnace for heating to compacting temperature, rapid removal of the heated charge from the furnace, and continuous transport to and loading within a fluid pressure vessel for compacting. In this manner, the charge is rapidly transferred from furnace to fluid pressure vessel, which eliminates the need for additional heating of the charge within the fluid pressure vessel. This, as earlier described, adds considerably to the economy of the operation. In addition,.by having a plurality of furnaces, as described herein, and by eliminating the need for heating within the autoclave it is possible to have a single autoclave fed by a plurality of furnaces and operating on a short-sequence compacting cycle. This enhances considerably the economy of the overall operation.

It is to be understood that the terms charge or furnace charge as used herein refer to material placed in the furnace for heating either with or without a container. In some applications material to be heated may be partially compacted when placed in the furnace and thus acontainer would not be required as with uncompacted powdered material.

We claim:

1. A furnace, particularly adapted for heating powder-metal charges to elevated temperatures suitable for compacting to form powdered metal articles, said furnace comprising an elongated, vertically disposed furnace chamber surrounded by heat-insulating material, a top of heat insulating material with an orifice in axial alignment with said furnace chamber, said orifice being selectively opened and closed by a lid selectively positionable between open and closed positions, whereby a charge may be vertically inserted and vertically withdrawn with respect to said furnace chamber, a pedestal, means for moving said pedestal vertically within said furnace chamber selectively between a position adjacent the top of said furnace chamber and a position adjacent the bottom of said chamber, whereby with said lid in the open position and said pedestal adjacent the chamber top a furnace charge for heating may be placed on said pedestal and lowered to the bottom pedestal position for heating upon closing of said lid, and means for supplying heat to said furnace chamber.

2. The furnace of claim 1 wherein said means for moving said pedestal includes a vertically extending shaft connected at an upper end thereof to said pedestal and drive means for moving said shaft and associated pedestal selectively axially into and out of said furnace chamber.

3. The furnace of claim 2 wherein said shaft has means for circulation of coolant therein, whereby said shaft is protected against heat damage.

4. The furnace of claim 2 wherein said drive means includes a counterweighted chain connected to said vertically extending shaft adjacent a lower end thereof and a pulley interposed between the connection to said shaft and a counterweight fastened to said chain.

5. The furnace of claim 2 wherein a plurality of vertically spaced guide means are provided in association with said shaft for guiding said shaft axially during movement thereof.

6. The furnace of claim 5 wherein said guide means comprise a plurality of idler rolls in contact with said shaft.

7. The furnace of claim 1 wherein said pedestal includes a heat-resistant alloy casing.

8. The furnace of claim 1 wherein said pedestal includes heat-insulating material, whereby heat loss from said furnace through said pedestal is minimized.

9. The furnace of claim 1 wherein said pedestal includes a casing of a heat-resistant alloy for supporting said charge, said casing enclosing a quantity of heatinsulating material.

10. The furnace of claim 1 wherein said means for supplying heat to said furnace chamber comprises a plurality of resistance heating elements.

11. The furnace of claim 10 wherein said resistance heating elements are provided along the entire length of said furnace and means are provided for independent supply of electrical current to selected heating elements.

12. The furnace of claim 11 wherein means are provided for independent supply of electrical current to selected heating elements adjacent the ends and midportion of said furnace chamber.

13. The furnace of claim 12 wherein means are provided for determining the temperature of said furnace chamber for areas adjacent the ends and mid-portion thereof, with an area of independent temperature -determination corresponding to each area adjacent said heating elements having independent current supply.

14. The furnace of claim 1 wherein said top is unitarily removable and is mounted on said heat-insulating material surrounding said furnace chamber, said top providing for exposure of and access to said heatinsulating material upon removal of said top.

15. The furnace of claim 1 wherein said orifice and said furnace chamber are annular with said orifice and lid being correspondingly tapered axially and inwardly toward said furnace chamber.

16. The furnace of claim 1 wherein said lid is selectively positionable between said open and closed positions within an orifice in axial alignment with said furnace chamber.

17. The furnace of claim 16 wherein said lid comprises two movable sections.

18. The furnace of claim 17 wherein said movable sections of said lid are provided with means for simultaneously moving said sections upwardly and out of engagement with said orifice and away from the axis thereof.

19. The furnace of claim 18 wherein said means for moving said sections includes for each section a pivot link connected at one end to a drive shaft and at the opposite end to a pivotal connection to said section.

20. The furnace of claim 19 wherein said means for moving said sections further includes an independent drive for each section with each drive connected to said drive shaft of said section. 4

21. The furnace of claim 16 wherein said lid and orifice are annular and are correspondingly tapered axially and inwardly toward said furnace chamber.

22. The furnace of claim 21 wherein said lid comprises two independently movable sections with each section including two parallel, spaced-apart plates separated by a core of heat-insulating material and means for securing said heat-insulating material between said plates.

23. The furnace of claim 22 wherein said means for securing said heat-insulating material between said plates includes at least one tie bolt secured to and extending between said plates and through said heatinsulating material.

24. The furnace of claim 1 wherein said furnace chamber conforms substantially to the shape of said charge.

25. The furnace of claim 24 wherein said charge includes metal in powder form within a container.

26. The furnace of claim 25 wherein said container and furnace chambers are generally cylindrical.

27. The furnace of claim 25 wherein said lid when in the closed position provides an opening therethrough to the exterior of said furnace through which extends a stem communicating with the interior of said container when said container is positioned for heating a charge may be vertically inserted and vertically withdrawn with respect to said furnace chamber, a pedestal, a vertically extending shaft connected at an upper end thereof to said pedestal, a counter-weighted chain connected to said shaft adjacent a lower endvthereof, a pulley interposed between the connection to said shaft and a counterweight fastened to said chain, drive means in driving engagement with said pulley for selectively rotating said pulley in opposite directions and thereby selectively axially raising and lowering said shaft and associated pedestal vertically within said furnace chamber selectively between a position adjacent the top of said furnace chamber and a position adjacent the bottom of said furnace chamber, whereby with said lid in the open position and said pedestal adjacent the furnace chamber top a furnace charge for heating may be placed on said pedestal and lowered to the bottom pedestal position for heating upon closing of said lid, and means for supplying heat to said furnace chamber.

29. The furnace of claim 28 wherein said pedestal includes a casing of a heat-resistant alloy for supporting said charges, said casing enclosing a quantity of heatinsulating material.

30. The furnace of claim 29 wherein said means for supplying heat to said furnace chamber comprise a plu rality of resistance heating elements provided along the entire length of said furnace, means for independent supply of electrical current to selected heating elements adjacent the ends and mid-portion of said furnace chamber and means for determining the temperature of said furnace chamber at areas adjacent the ends and mid-portion of said furnace chamber, with an area of temperature determination corresponding to each area adjacent said heating elements having independent current supply.

31. The furnace of claim 28 wherein said top is unitarily removable and provides for exposure of and access to said heat-insulating material upon removal of said top and said lid comprises two movable sections having means for simultaneously moving said sections upwardly and out of engagement with said orifice and away from the axis thereof.

32. The furnace of claim 31 wherein said furnace chamber, orifice and lid are annular with said furnace chamber conforming substantially to the shape of said charge. 

1. A furnace, particularly adapted for heating powder-metal charges to elevated temperatures suitable for compacting to form powdered metal articles, said furnace comprising an elongated, vertically disposed furnace chamber surrounded by heat-insulating material, a top of heat insulating material with an orifice in axial alignment with said furnace chamber, said orifice being selectively opened and closed by a lid selectively positionable between open and closed positions, whereby a charge may be vertically inserted and vertically withdrawn with respect to said furnace chamber, a pedestal, means for moving said pedestal vertically within said furnace chamber selectively between a position adjacent the top of said furnace chamber and a position adjacent the bottom of said chamber, whereby with said lid in the open position and said pedestal adjacent the chamber top a furnace charge for heating may be placed on said pedestal and lowered to the bottom pedestal position for heating upon closing of said lid, and means for supplying heat to said furnace chamber.
 2. The furnace of claim 1 wherein said means for moving said pedestal includes a vertically extending shaft connected at an upper end thereof to said pedestal and drive means for moving said shaft and associated pedestal selectively axially into and out of said furnace chamber.
 3. The furnace of claim 2 wherein said shaft has means for circulation of coolant therein, whereby said shaft is protected against heat damage.
 4. The furnace of claim 2 wherein said drive means includes a counterweighted chain connected to said vertically extending shaft adjacent a lower end thereof and a pulley interposed between the connection to said shaft and a counterweight fastened to said chain.
 5. The furnace of claim 2 wherein a plurality of vertically spaced guide means are provided in association with said shaft for guiding said shaft axially during movement thereof.
 6. The furnace of claim 5 wherein said guide means comprise a plurality of idler rolls in contact with said shaft.
 7. The furnace of claim 1 wherein said pedestal includes a heat-resistant alloy casing.
 8. The furnace of claim 1 wherein said pedestal includes heat-insulating material, whereby heat loss from said furnace through said pedestal is minimized.
 9. The furnace of claim 1 wherein said pedestal includes a casing of a heat-resistant alloy for supporting said charge, said casing enclosing a quantity of heat-insulating material.
 10. The furnace of claim 1 wherein said means for supplying heat to said furnace chamber comprises a plurality of resistance heating elements.
 11. The furnace of claim 10 wherein said resistance heating elements are provided along the entire length of said furnace and means are provided for independent supply of electrical current to selected heating elements.
 12. The furnace of claim 11 wherein means are provided for independent supply of electrical current to selected heating elements adjacent the ends and mid-portion of said furnace chamber.
 13. The furnace of claim 12 wherein means are provided for determining the temperature of said furnace chamber for areas adjacent the ends and mid-portion thereof, with an area of independent temperature determination corresponding to each area adjacent said heating elements having independent current supply.
 14. The furnace of claim 1 wherein said top is unitarily removable and is mounted on said heat-insulating material surrounding said furnace chamber, said top providing for exposure of and access to said heat-insulating material upon removal of said top.
 15. The furnace of claim 1 wherein said orifice and said furnace chamber are annular with said orifice and lid being correspondingly tapered axially and inwardly toward said furnace chamber.
 16. The furnace of claim 1 wherein said lid is selectively positionable between said open and closed positions within an orifice in axial alignment with said furnace chamber.
 17. The furnace of claim 16 wherein said lid comprises two moVable sections.
 18. The furnace of claim 17 wherein said movable sections of said lid are provided with means for simultaneously moving said sections upwardly and out of engagement with said orifice and away from the axis thereof.
 19. The furnace of claim 18 wherein said means for moving said sections includes for each section a pivot link connected at one end to a drive shaft and at the opposite end to a pivotal connection to said section.
 20. The furnace of claim 19 wherein said means for moving said sections further includes an independent drive for each section with each drive connected to said drive shaft of said section.
 21. The furnace of claim 16 wherein said lid and orifice are annular and are correspondingly tapered axially and inwardly toward said furnace chamber.
 22. The furnace of claim 21 wherein said lid comprises two independently movable sections with each section including two parallel, spaced-apart plates separated by a core of heat-insulating material and means for securing said heat-insulating material between said plates.
 23. The furnace of claim 22 wherein said means for securing said heat-insulating material between said plates includes at least one tie bolt secured to and extending between said plates and through said heat-insulating material.
 24. The furnace of claim 1 wherein said furnace chamber conforms substantially to the shape of said charge.
 25. The furnace of claim 24 wherein said charge includes metal in powder form within a container.
 26. The furnace of claim 25 wherein said container and furnace chambers are generally cylindrical.
 27. The furnace of claim 25 wherein said lid when in the closed position provides an opening therethrough to the exterior of said furnace through which extends a stem communicating with the interior of said container when said container is positioned for heating within said furnace chamber.
 28. A furnace, particularly adapted for heating powder-metal charges to elevated temperatures suitable for compacting to form powdered metal articles, said furnace comprising an elongated, vertically disposed furnace chamber surrounded by heat-insulating material, a top of heat insulating material with an orifice in axial alignment with said furnace chamber, said orifice being selectively opened and closed by a lid selectively positionable between open and closed positions, whereby a charge may be vertically inserted and vertically withdrawn with respect to said furnace chamber, a pedestal, a vertically extending shaft connected at an upper end thereof to said pedestal, a counter-weighted chain connected to said shaft adjacent a lower end thereof, a pulley interposed between the connection to said shaft and a counterweight fastened to said chain, drive means in driving engagement with said pulley for selectively rotating said pulley in opposite directions and thereby selectively axially raising and lowering said shaft and associated pedestal vertically within said furnace chamber selectively between a position adjacent the top of said furnace chamber and a position adjacent the bottom of said furnace chamber, whereby with said lid in the open position and said pedestal adjacent the furnace chamber top a furnace charge for heating may be placed on said pedestal and lowered to the bottom pedestal position for heating upon closing of said lid, and means for supplying heat to said furnace chamber.
 29. The furnace of claim 28 wherein said pedestal includes a casing of a heat-resistant alloy for supporting said charges, said casing enclosing a quantity of heat-insulating material.
 30. The furnace of claim 29 wherein said means for supplying heat to said furnace chamber comprise a plurality of resistance heating elements provided along the entire length of said furnace, means for independent supply of electrical current to selected heating elements adjacent the ends and mid-portion of said furnace chamber and means for determining the temperature of said furnace chamber at areas adjacent the enDs and mid-portion of said furnace chamber, with an area of temperature determination corresponding to each area adjacent said heating elements having independent current supply.
 31. The furnace of claim 28 wherein said top is unitarily removable and provides for exposure of and access to said heat-insulating material upon removal of said top and said lid comprises two movable sections having means for simultaneously moving said sections upwardly and out of engagement with said orifice and away from the axis thereof.
 32. The furnace of claim 31 wherein said furnace chamber, orifice and lid are annular with said furnace chamber conforming substantially to the shape of said charge. 